The present invention relates to a control system for a throttle valve actuating device including a throttle valve of an internal combustion engine and an actuator for actuating the throttle valve.
One known control system for controlling a throttle valve actuating device including a motor for actuating the throttle valve and springs for energizing the throttle valve is disclosed in Japanese Patent Laid-open No. Hei 8-261050. In this control system, the throttle valve actuating device is controlled with a PID (Proportional, Integral, and Differential) control according to a throttle valve opening detected by a throttle valve opening sensor.
Since the throttle valve actuating device includes a dead time element which delays the throttle valve movement, the PID control by the above-described conventional control system may easily become unstable if the control gain of the PID control according to the detected throttle valve opening is set to a large value. Therefore, it is necessary to set the control gain to a value which is sufficiently small so that the control may not become unstable. However, this results in a low response speed.
It is therefore an object of the present invention to provide a control system for a throttle valve actuating device, which can improve the response speed by expanding the stability margin of the control.
To achieve the above object, the present invention provides a control system for a throttle valve actuating device (10) including a throttle valve (3) of an internal combustion engine and actuating means (6) for actuating the throttle valve (3). The control system includes predicting means (23) for predicting a future throttle valve opening (PREDTH) and controls the throttle actuating device (10) according to the throttle valve opening (PREDTH) predicted by the predicting means (23) so that the throttle valve opening (TH) coincides with a target opening (THR).
With this configuration, the throttle actuating device is controlled according to the future throttle valve opening predicted by the predicting means. Accordingly, the stability margin of the control can be expanded although the throttle valve actuating device includes a dead time element. As a result, the control gain can be set to a larger value to thereby improve the control response speed.
Preferably, the throttle valve actuating device (10) is modeled to a controlled object model which includes a dead time element, and the predicting means (23) predicts a throttle valve opening after the elapse of a dead time (d) due to the dead time element, based on the controlled object model.
With this configuration, the throttle valve actuating device (10) is modeled to the controlled object model including a dead time element, and the throttle valve opening after the elapse of a dead time is predicted based on the controlled object model. Accordingly, compensation of the dead time in the throttle valve actuating device can accurately be performed.
Preferably, the control system further includes identifying means (22) for identifying at least one model parameter (a1, a2, b1, c1) of the controlled object model. The predicting means (23) predicts the throttle valve opening (PREDTH) using the at least one model parameter (a1, a2, b1, c1) identified by the identifying means (22).
With this configuration, the throttle valve opening is predicted using one or more model parameter identified by the identifying means. Accordingly, it is possible to calculate an accurate predicted throttle valve opening even when the dynamic characteristic of the throttle valve actuating device has changed due to aging or a change in the environmental condition.
Preferably, the control system further includes a sliding mode controller (21) for controlling the throttle valve actuating device (10) with a sliding mode control according to a throttle valve opening (PREDTH) predicted by the predicting means (23).
With this configuration, the throttle valve actuating device is controlled with the sliding mode control having good robustness. Accordingly, good stability and controllability of the control can be maintained even when there exists a modeling error (a difference between the characteristics of the actual plant and the characteristics of the controlled object model) due to a difference between the actual dead time of the throttle valve actuating device and the dead time of the controlled object model.
Preferably, the sliding mode controller (21) controls the throttle valve actuating device (10) using the at least one model parameter (a1, a2, b1, c1) identified by the identifying means (22).
With this configuration, the throttle valve actuating device is controlled by the sliding mode controller using one or more model parameter identified by the identifying means. Accordingly, the modeling error can be made smaller so that the controllability is further improved.
Preferably, the control input (Usl) from the sliding mode controller (21) to the throttle valve actuating device (10) includes an adaptive law input (Uadp).
With this configuration, better controllability is obtained even in the presence of disturbance and/or the modeling error.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate embodiments of the present invention by way of example.